Jan Bültmann

Mechanical response of TiAl6V4 lattice structures manufactured by selective laser melting in quasistatic and dynamic compression tests

This paper focusses on the investigation of the mechanical properties of lattice structures manufactured by selective laser melting using contour-hatch scan strategy. The motivation for this research is the systematic investigation of the elastic and plastic deformation of TiAl6V4 at different strain rates. To investigate the influence of the strain rate on the mechanical response (e.g., energy absorption) of TiAl6V4 structures, compression tests on TiAl6V4-lattice structures with different strain rates are carried out to determine the mechanical response from the resulting stress-strain curves. Results are compared to the mechanical response of stainless steel lattice structures (316L). It is shown that heat-treated TiAl6V4 specimens have a larger breaking strain and a lower drop of stress after failure initiation. Main finding is that TiAl6V4 lattice structures show brittle behavior and low energy absorption capabilities compared to the ductile behaving 316L lattice structures. For larger strain rates, ultimate tensile strength of TiAl6V4 structures is more than 20% higher compared to lower strain rates due to cold work hardening.

Direct photonic production: towards high speed additive manufacturing of individualized goods

World market competition currently boosts trends like mass customization and open innovation which result in a demand for highly individualized products at costs matching or beating those of mass production. This work focus on the resolution of the production related dilemma between scale and scope, e.g. either the low-cost production of high quantities or the high-end and thus cost-intensive low-volume production of individualized goods. One of the areas of greatest potential for the resolution of this dilemma are rapid manufacturing (RM) technologies due to their almost infinite geometrical variability and freedom of design without the need for part-specific tooling. Selective Laser Melting (SLM) is one of the RM technologies that additionally provides series identical mechanical properties without the need for downstream sintering processes, etc. However, the state-of-the-art process and cost efficiency is not yet suited for series production. In order to improve this efficiency and enable SLM to enter series production it is indispensable to increase the build rate significantly by means of increased laser power and larger beam diameters. To exploit this potential, a new generation production machine including a kW laser and an optical multi-beam system is developed and experimental results and real life components are shown.

Investigation on Incremental Sheet Forming Combined with Laser Heating and Stretch Forming for the Production of Lightweight Structures

Asymmetric Incremental Sheet Forming (AISF) is a process for the flexible production of sheet metal parts. In AISF, a part is obtained as the sum of localized plastic deformations produced by a simple forming tool that, in most configurations, moves under CNC control. Flexible processes with low tooling effort like AISF are suitable for sectors with small lot sizes but premium products, e.g. for the aviation and the automotive sector. Four main process limits restrict the range of application of AISF and its take-up in industry. These are: (i) material thinning, (ii) limited geometrical accuracy, (iii) the process duration and (iv) the calculation time and accuracy of process modelling. Moreover, the material spectrum of AISF for structural parts is mostly restricted to cold workable materials like steel and aluminum. This paper presents some new investigations of incremental sheet forming combined with laser heating or stretch forming as possible hybrid approaches to overcome the above mentioned limitations of AISF. These hybrid incremental sheet forming processes can increase the technological and economical potentials of AISF. A possible application is the fabrication of lightweight sheet metal parts as individual parts or small batches, e.g. for the aerospace industry. The present study provides a short overview of the state of the art of AISF, introduces the new hybrid process variations of AISF and compares the capabilities of the hybrid processes and the standard AISF process. Finally, two examples for applications are presented: (i) the production of a part used in an airplane for which the manufacturing steps consist of die manufacture, sheet metal forming by means of stretch forming combined with AISF and a final trimming operation using a single hybrid machine set-up; (ii) laser-assisted AISF for magnesium alloys.

Exploiting Process-Related Advantages of Selective Laser Melting for the Production of High-Manganese Steel

Metal additive manufacturing has strongly gained scientific and industrial importance during the last decades due to the geometrical flexibility and increased reliability of parts, as well as reduced equipment costs. Within the field of metal additive manufacturing methods, selective laser melting (SLM) is an eligible technique for the production of fully dense bulk material with complex geometry. In the current study, we addressed the application of SLM for processing a high-manganese TRansformation-/TWinning-Induced Plasticity (TRIP/TWIP) steel. The solidification behavior was analyzed by careful characterization of the as-built microstructure and element distribution using optical and scanning electron microscopy (SEM). In addition, the deformation behavior was studied using uniaxial tensile testing and SEM. Comparison with conventionally produced TRIP/TWIP steel revealed that elemental segregation, which is normally very pronounced in high-manganese steels and requires energy-intensive post processing, is reduced due to the high cooling rates during SLM. Also, the very fast cooling promoted ε- and α’-martensite formation prior to deformation. The superior strength and pronounced anisotropy of the SLM-produced material was correlated with the microstructure based on the process-specific characteristics.

Scalability of the mechanical properties of selective laser melting produced micro-struts

Selective laser melting (SLM) is a manufacturing process that builds up metallic or ceramic parts layer by layer directly from 3D-computer-aided design data, offering, for example, the advantage of imposing little restrictions in terms of geometric complexity. One of the main challenges of the SLM process is to improve its efficiency by increasing the build rate of the process and thereby decreasing time and cost. One way of achieving this is increasing the applied laser power and beam diameter, thereby melting more volume in a shorter period of time. Another option of improving efficiency is reducing the volume of the material which has to be melted, made possible by the aforementioned limitless geometric freedom offered by the SLM process. Hereby, one can generate hollow parts for better exploitation and adaption of the volume to specific load cases. Large volumes can be replaced by lattice structures with a certain volume fraction, saving weight and production time by maintaining the stiffness of the s...

Hybrid Production Systems

While virtual product development allows great freedom in terms of design, actual development processes are rather restricted. Those boundary conditions are at best hardly possible to exert influence on. Therefore, future research has to focus both on the realisation of the concept of one-piece-flow while simultaneously increasing flexibility and productivity and on the technological advancement. Hence, hybridisation of manufacturing processes is a promising approach, which often allows tapping potentials in all the aforementioned dimensions.

Direct, Mold-Less Production Systems

Additive Manufacturing (AM) technologies in general—and in particular, Selective Laser Melting (SLM)—are characterized by a fundamentally different relationship with respect to costs, lot size, and product complexity compared to conventional manufacturing processes. There is no increase of costs for small lot sizes (in contrast to mold-based technologies) and none for shape complexity either (in contrast to subtractive technologies). Thus, only the holistic development of a direct, mold-less production system that takes all relevant interdependencies along the product creation chain into account provides the full economic, ecologic and social benefits of AM technologies in future production. The following six subjects of the product creation chain were examined: (i) New business models and customer willingness to pay for AM parts are revealed. (ii) The Product Production System (PPS) was totally revised regarding the adoption of SLM technology into conventional manufacturing environment. (iii) The SLM manufacturing costs were examined regarding different machine configurations. (iv) A high-power SLM process was developed for enhancing the process productivity. (v) High manganese steel was qualified for the SLM process. (vi) Finally, two lattice structure types and a design methodology for customer parts were developed.